The invention generally relates to methods for manufacturing pot-shaped pressure vessels.
More specifically, the invention relates to a method for manufacturing a pot-shaped pressure vessel, in particular an air spring pot for a vehicle, comprising the following steps:
providing a pot, which comprises a bottom, which comprises at least one aperture,
providing at least one screw, which comprises a head and a shank,
inserting, the shank of the at least one screw through the aperture from an inside of the pot, so that the shank of the screw protrudes from an outside of the bottom and
firmly joining the screw to the bottom of the pot.
The invention further generally relates to pot-shaped pressure vessels.
More specifically, the invention further relates to a pot-shaped pressure vessel, in particular an air spring pot for a vehicle, comprising a pot, which comprises a bottom, which comprises at least one aperture, and at least one screw, which comprises a head and a shank, the screw being inserted through the aperture from an inside of the pot, so that the shank of the screw protrudes from an outside of the bottom, and the screw being firmly joined to the bottom of the pot.
Without limiting the generality, the present invention will be described with reference to a pot-shaped pressure vessel, which is used as an air spring pot of an air spring for a vehicle.
Air springs are used in vehicle construction instead of or in addition to steel springs for the suspension of the vehicle body. Air springs are also used in vehicle construction for ride height adjustment of the body.
In the case of air springs the suspension is achieved by a volume of gas. The volume of gas is here situated in a pot-shaped pressure vessel, referred to as an air spring pot. At its upper end, as fitted in a vehicle, the air spring pot, which is usually made of sheet steel, comprises a bottom, from which a pot wall extends downwards approximately perpendicularly to the bottom. A bellows is usually affixed to the lower end of the pot wall, as fitted in a vehicle.
For fitting the air spring pot in a vehicle one or more screws are firmly joined to the bottom of the pot at the bottom of the pot. When the screws are fixed to the bottom of the pot, the respective shank of each screw protrudes approximately perpendicularly to the bottom from the outside thereof, that is to say upwards when the air spring pot is fitted in a vehicle. The screws serve to fix the air spring pot to the vehicle body, or more precisely to the spring dome. The screws fixed to the bottom of the air spring pot here have to fit into a predefined hole pattern in the spring dome and must therefore be correctly positioned and aligned according to the hole pattern.
In the prior art various methods are now known for joining the screws to the bottom of the air spring pot.
In a first known method of attaching the screws to the bottom of the air spring pot the heads of the screws are placed on the outside of the bottom and firmly joined to the bottom by friction welding. Since in friction welding the screws are moved relative to the bottom of the pot, in order for the resulting friction to bring about the welding fusion process, this approach has the disadvantage that the screws cannot be precisely positioned in the correct position relative to the hole pattern. Moreover if the bottom of the pot does not have the correct surface orientation owing to production tolerances at the points at which the screws are to be affixed, the shanks of the screws may furthermore also have an incorrect orientation relative to the hole pattern, that is to say an axial error. This known method of joining the screws to the bottom of the air spring pot is therefore subject to tolerances. A further disadvantage to attaching the screws onto the outside of the bottom is that the screw heads protrude from the outside of the bottom. In this method of affixing the screws to the bottom, therefore, depressions or troughs are provided in the bottom of the pot at the points where the screws are to be affixed, so that the screw heads do not protrude beyond the general level of the outside of the bottom. In this case, however, height tolerances of the screw heads may nevertheless be a factor, that is to say tolerances of the depressions in the bottom of the pot may mean that the screw heads still protrude beyond the general level of the outside of the bottom, thereby making it more difficult to fit the air spring pot in the correct position on the spring dome. The advantage of attaching the screws to the outside of the bottom of the air spring pot, however, is that the bottom of the pot as a whole constitutes a closed and therefore pressure-tight surface.
In another known method for joining the screws to the bottom of the air spring pot, from which the method referred to in the introductory portion and the pressure vessel referred to in the introductory portion depart, the pot is provided in such a way that that the bottom has an aperture for each screw. In this case the shank of each screw is inserted through the respective aperture from the inside of the pot, until the face of the screw head facing the shank bears against the inside of the bottom of the pot. The screw head is then firmly joined to the inside of the bottom of the pot by metal-active gas-shielded (MAG) welding. Even in this known method for firmly joining the screws to the bottom of the air spring pot there is still the disadvantage that, in the event of incorrect orientations of the bottom of the pot, the shanks of the screws will have an axial error. With this known method there is furthermore the disadvantage that for welding use is made of a welding filler metal, which in uncontrolled cooling can give rise to incorrect positioning of the screw shanks. In the event of incorrect orientations of the pot bottom, it is not possible with this known method to control the alignment of the shanks of the screws according to the hole pattern in order to compensate for incorrect positioning of the bottom, because as the welding filler metal cools the respective screw head is drawn uncontrollably against the bottom of the pot. In addition, in the deposit-welding process, porosity or air inclusions can form, which may lead to leaks in the area of the respective aperture in the bottom of the air spring pot, with the result that the pot is not pressure-tight and therefore not suitable as an air spring pot.
One approach, which represents a modification of the known method referred to above, is to likewise insert the screw shanks through the respective aperture in the bottom of the air spring pot from the inside and then to press the screws into the aperture together with an additional sealing element or sealant. Here too, however, there is still the disadvantage of insufficient allowance for tolerances, because it is not sufficiently possible to purposely align the shanks of the screws in the event of incorrect orientations of the bottom of the air spring pot.